1. Field of the Invention
The present invention relates to a method of fabricating a phase change memory (PCM) and a phase change memory thus formed, and particularly to a phase change memory with a heater structure in a tapered shape.
2. Description of the Prior Art
A PCM is a memory device using the phase change capability of so-called phase change material whose phase would change in response to external thermal stress, e.g., amorphous to crystalline, as a mechanism to store data. The amorphous state of the phase change material generally exhibits greater specific resistance than the crystalline state, and using this difference of specific resistance it is possible to determine whether data recorded by the phase change material is a logic “1” or a logic “0” by detecting a voltage change and/or a current change caused by difference of this specific resistance.
A representative example of a phase change material may include a compound containing germanium (Ge), tellurium (Te) and stibium (Sb)—generally referred to as GST. A PCM using this phase change material can have benefits of being non-volatile and with a data retention of more than 10 years, a short written time of less than 100 nanoseconds, and a low write power of, for example, 3V×1 mA. Another benefit of PCM memory is its high durability to allow billions of cycles of data writing and erasing. In addition, a PCM device has a good scalability.
FIG. 1 shows a cross sectional view of a conventional PCM. The PCM 10 includes a lower electrode 12, a heater 14, a phase change material layer 16, and an upper electrode 18. The active region 15 of the phase change material layer 16 is heated up by the amount of current that flows through the interface between the heater 14 and the phase change material layer 16. The active region 15 of the phase change material layer 16 is changed into an amorphous state or a crystalline state in accordance with the heating efficiency and duration of the current.
For a PCM device, it is desirable to reduce the size of a contact area between the electrode and the phase change material, so as to increase local heating effect. Accordingly, a novel PCM device with a novel heater structure having a small contact area to the phase change material is still desirable.